Google, Yahoo, Facebook and several other large Web companies today joined a growing chorus of strong opposition to proposed legislation that aims to curb online IP and copyright theft by foreign sites.

Critics say both bills are overly broad and mostly serve the interests of Hollywood and the U.S. music industry.

SOPA, currently winding its way through the U.S. House of Representatives, has drawn the most ire because it is widely seen as the most draconian and caters more to the entertainment industry than its U.S. Senate counterpart.

In a letter sent to the House and Senate Judiciary Committees, Google, Yahoo and others expressed concern over the legislation's "new uncertain liabilities" and "private rights of action."

While the companies agree that new enforcement tools are needed to combat rogue websites dedicated to copyright infringement and counterfeiting, they say proposed bills go too far.

"We are concerned that these measures pose a serious risk to our industry's continued track record of innovation and job creation, as well as to our Nation's cybersecurity," the letter read. "We cannot support these bills as written and ask that you consider more targeted ways to combat foreign 'rogue' websites."

Both bills aim to combat what their supporters say are rogue websites based outside the U.S that focus on the illegal sale of copyrighted content and counterfeit U.S. goods such as prescription drugs.

The Digital Millennium Copyright Act (DMCA) currently allows copyright owners and IP owners to ask sites like YouTube, Facebook or EBay to take down content that are believed to violate copyright and IP protection laws.

DMCA does not hold ISPs directly responsible for the content on their networks. Both the Protect IP Act and SOPA would hold them directly responsible for hosting such content on their sites.

The SOPA legislation would also allow copyright holders and IP owners to ask payment processing companies such as MasterCard and PayPal, as well as advertising networks, to terminate their services to any site. ISPs that comply with the requests would receive full immunity under SOPA. Companies that don't comply with the requests could face legal action from copyright and IP holders.

Some opponents say that the SOPA law is worded in a way that would allow content owners to shut down websites that host even one page of illegal content. For instance, an auction website such as EBay would theoretically be in violation of SOPA if someone listed a counterfeit item for sale.

Opponents are concerned that the private right of action allowed under the bill undermines Safe Harbor provisions in DMCA. They also worry the innovation that created sites like YouTube would be stifled.

At a news conference tday, Computers and Communications Industry Association (CCIA) officials said SOPA poses a cybersecurity threat and that it would require ISPs to interfere with secure connections between a users and websites.

"[SOPA] may adversely affect every company doing business online, from Sears to Twitter. In effect it will impose and privatize a national censorship regime," the trade association said in a statement released Tuesday.

Growing opposition to SOPA is not surprising said Corryne McSherry, intellectual property director at the Electronic Frontier Foundation. "The groups that drafted this bill did so without input from the numerous communities it would affect, but they couldn't keep it under wraps forever," she said.

"As for complaints that the current system doesn't work, one has to wonder when big media is going to learn that the only successful response to the problem of online infringement is to offer a better alternative," she said.

Supporters of the bills, including the Motion Picture Association of America, the Recording Industry Association of America, Pfizer and dozens of trade groups, insist that the measures target only egregious offenders based outside the U.S.

The supporters insist that the concerns of opponents are overstated and misdirected.